https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108299
--- Comment #3 from Andrea Griffini <agriff at tin dot it> ---
Thread storage duration is different from static storage duration.
The text I found on the topic is different from the one you are linking,
but even in this version (that is indeed more permissive) it's explicitly
stated that a thread_local variable must be initialized before any other
thread_local variable is accessed in the same compilation unit.
> it is implementation-defined whether the dynamic initialization of a
> non-block non-inline variable with thread storage duration is sequenced
> before the first statement of the initial function of a thread or is deferred.
> --------------------------------------------------------------------
> If it is deferred, the initialization associated with the entity for thread
> t is sequenced before the first non-initialization odr-use by t of any
> non-inline variable with thread storage duration defined in the same
> translation unit as the variable to be initialized.
> --------------------------------------------------------------------
> It is implementation-defined in which threads and at which points in
> the program such deferred dynamic initialization occurs.
g++ doesn't seem to follow the rule
#include <stdio.h>
thread_local int flag = ([](){
printf("HERE!\n"); // This initialization never happens
return 1;
})();
thread_local int flag2;
int main() {
printf("Hello, world.\n");
flag2 = 0; // accesses another thread_local variable in same compilation
unit
return 0;
}
